The temperature dependence of insulation characteristics of transformer oil at low temperatures

This paper presents the test methods of studying insulation characteristics of transformer oil at low temperatures. Karamay DB-45 transformer oils were selected as the initial specimens. Oil samples of different quality indexes were obtained after processing by the vacuum oil purifier. Each kind of oil sample was carried out experiments on insulating properties at low temperatures. The temperature dependence of the dielectric strength of transformer oil at low temperatures (-20°C~10°C) is obtained by statistical analysis of test results. (1)The relation curves of breakdown voltage vs. temperature show “U”-type features when the water content is high. (2)Water content is the main influence factor of breakdown voltage of transformer oils. (3)In general, the values of the transformer oil breakdown voltage measured at room temperature do not represent their breakdown voltage level at low temperatures. (4)If the oil samples meet the requirements of the current EHV/UHV transformer oil standards, the impact of temperature on the breakdown voltage is very small at low temperatures. (5)The permittivity and the dielectric loss factor of transformer oils little change in the range of -20°C~10°C.